The Question:

Which U.S. city is called "The Emerald City?"

The Answer:

The City of
Seattle lies in western Washington between two bodies
of water—Puget Sound on the west and Lake Washington on the east. The
city was given the nickname by tourism officials, who were promoting
Seattle as "The Emerald City" in the mid-1980s. This is mostly due to
the lush, green forests of Washington and the more than 6,000 acres of
parks within the city limits.

You can find more information about the city at its official
website, Seattle.gov.